Binder composition for mold making, binder/curing agent composition for mold making, sand composition for mold making, and process of making mold

ABSTRACT

Sand compositions containing a binder composition and a curing agent, in which the binder composition comprises (a) a binder comprising an acid-curable resin and (b) from 0.5 to 63.0% by weight, based on the binder composition, of at least one curing accelerator selected from compounds represented by formula (1): ##STR1## wherein X 1 , X 2  each represent a hydrogen atom, a methyl group or an ethyl group; 
     exhibit an increased curing rate to provide a casting mold having an increased initial strength.

This is a Division of application Ser. No. 08/291,065 filed on Aug. 17,1994 now U.S. Pat. No. 5,491,180.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a binder composition for mold makingwhich is useful in making a casting mold, especially a self-hardeningmold, a composition for casting mold making comprising the bindercomposition and a specific curing agent composition, a sand compositionfor mold making containing the binder composition or binder/curing agentcomposition, and a process for making a mold using the sand composition.

2. Discussion of the Background

Self-hardening molds have conventionally been produced by mixing agranular refractory material, such as silica sand, with a bindercomprising an acid-curable resin and a curing agent, charging themixture in a pattern, and causing the binder to cure.

In an early stage of the art, a thick solution of phosphoric acid hadbeen widely used as a curing agent for the acid-curable resin. Forexample, JP-B-39-1543 (the term "JP-B" as used herein means an "examinedJapanese patent publication") discloses the use of an acid-curableresin, such as an acid-curable furan resin, as a binder and use of anaqueous solution of an acid, e.g., phosphoric acid, as a curing agentfor the binder. JP-A-47-16324 (the term "JP-A" as used herein means an"unexamined published Japanese patent application") discloses the use ofphosphorous pentoxide (P₂ O₅) as a curing agent.

However, since the conventional binders generally have a low curingrate, the strength of the mold obtained in the initial stage (initialstrength) is low. That is, a long time is required from the filling ofthe pattern to the removal of the cured mold from the pattern, resultingin poor utilization of the pattern.

In order to overcome this disadvantage, an increase in the amount ofcuring agent has been attempted. However, if mold making is repeatedwhile using a large quantity of phosphoric acid as a curing agent,phosphorus is gradually accumulated in the reclaimed sand to a largequantity, which often causes casting defects, such as pinholes. Further,since the reclaimed sand absorbs moisture due to the accumulatedphosphorus, it tends to provide a casting mold having a deterioratedstrength.

For these reasons, an aromatic sulfonic acid, such as benzenesulfonicacid, toluenesulfonic acid or xylenesulfonic acid, which has highreactivity to increase the curing rate of an acid-curable resin has beenused as a curing agent in place of phosphoric acid. However, aromaticsulfonic acids decompose due to the heat of a casting material, wherebyit releases poisonous decomposition products, such as sulfur-containinggas. Therefore, the use of an aromatic sulfonic acid as a curing agentis detrimental to the working environment.

Hence, alteration of the kind of a binder itself has been attemptedinstead of increasing the amount of a curing agent or changing of thecuring agent. For example, JP-A-56-56753 proposes to incorporate, intofurfuryl alcohol, a resol type phenol-formaldehyde resin substantiallyfree from a mononuclear phenolic compound, a binuclear phenolic compoundor a methytol derivative thereof. The use of such a resol typephenol-formaldehyde resin substantially free from low-molecular weightresins as part of a binder brings about reduction in time required forhigh-molecular forming reaction, thereby improving mold strength in theinitial stage.

However, there remains a need for binder compositions for mold makingwhich provide a mold with high initial strength and do not suffer fromthe above-described drawbacks.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide novelbinder compositions for mold making, which comprise a conventionalbinder and provides a mold with a high initial strength.

It is another object of the present invention to provide bindercompositions for mold making which minimize the release of toxic gasesduring use.

It is another object of the present invention to provide bindercompositions for mold making which permit the reuse of reclaimed sandwithout causing defects or loss of strength in the casting mold.

It is another object of the present invention to provide binder/curingagent compositions for mold making which contains a curing agent andsuch a binder composition.

It is another object of the present invention to provide sandcompositions for mold making which contains sand and such a bindercompositions.

It is another object of the present invention to provide a process formaking a mold using such a sand composition.

These and other objects, which will become apparent during the followingdetailed description, have been achieved by the inventors' discoverythat a binder composition containing a specific curing acceleratorexhibits an increased curing rate on contact with a curing agent toprovide a mold with an increased initial strength. They also have foundthat a combination of such a binder composition and a specific curingagent composition provides a composition exhibiting a further increasedcuring rate while avoiding accumulation of a large quantity ofphosphorus in reclaimed sand and suppressing generation of poisonousdecomposition products, such as sulfur-containing gas. The presentinvention has been completed based on these findings.

Thus, the present invention provides a binder composition for moldmaking which comprises:

(a) a binder comprising an acid-curable resin, and

(b) from 0.5 to 63.0% by weight, based on the weight of the bindercomposition, of at least one curing accelerator selected from compoundsrepresented by formula (1): ##STR2## wherein X₁, X₂ each independentlyrepresent a hydrogen atom, a methyl group or an ethyl group.

The present invention further provides a binder/curing agent compositionfor mold making which comprises:

(i) a binder composition comprising:

(a) a binder comprising an acid-curable resin, and

(b) from 0.5 to 63.0% by weight, based on the total amount of binder (a)and curing accelerator (b), of at least one curing accelerator selectedfrom compounds represented by formula (1); and

(ii) a curing agent composition comprising a phosphorus-containingcompound and a sulfur-containing compound at such a weight ratio that aweight ratio of sulfur atoms to the total weight of phosphorus atoms andsulfur atoms is from 0.01 to 0.7.

The present invention furthermore provides a sand composition for moldmaking containing the above-mentioned binder composition orbinder/curing agent composition.

The present invention furthermost provides a process for making a moldby using the above-mentioned sand composition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The binder composition for molding making (hereinafter simply referredto as a binder composition) comprises (a) a binder comprising anacid-curable resin and (b) a curing accelerator.

Curing accelerator (b) is a compound represented by formula (1) or amixture of two or more of the compounds of formula (1). Preferredexamples of the compound of formula (1) include2,5-bishydroxymethylfuran (hereinafter sometimes referred to asbishydroxymethylfuran), 2,5-bismethoxymethylfuran (hereinafter sometimesreferred to as bismethoxymethylfuran), 2,5-bisethoxymethylfuran(hereinafter sometimes referred to as bisethoxymethylfuran),2-hydroxymethyl-5-methoxymethylfuran,2-hydroxymethyl-5-ethoxymethylfuran, and2-methoxymethyl-5-ethoxymethylfuran. Among them,2,5-bishydroxymethylfuran is more preferred since it is more reactivethan 2,5-bismethoxymethylfuran or 2,5-bisethoxymethylfuran inacceleration of the curing reaction of the binder comprising anacid-curable resin. The higher reactivity of 2,5-bishydroxymethylfuranis attributed to the methylol group which contributes to a curingreaction. More specifically, 2,5-bismethoxymethylfuran or the like isless reactive because its alkoxy group once undergoes hydrolysis to forma methylol group, which then contributes to a curing reaction. Althoughit is known that the reaction between furfuryl alcohol and formaldehydein the preparation of a furan resin is attended by formation of2,5-bishydroxymethylfuran as an initial condensation product (seeKOBUNSHI YAKUZAI NYUMON, published by Sanyo Chemical Industries, Co.,Ltd.), it has not yet come to be known that this2,5-bishydroxymethylfuran performs the function as a curing acceleratorfor an acid-curable resin used in mold making. The compound of formula(1) may be prepared in a known method as disclosed, for example, inBlanksma, Rec. Trav. Chim., 29, 403 (1910), Middendorp., Rec. Tray.Chim., 38, 1 (1919), Newth and Wiggins, Research (London), 3, Suppln.50-1 (1950), or C. A., 44, 6848 (1950).

Curing accelerator (b) is preferably used in an amount of from 0.5 to63.0% by weight, preferably from 1.8 to 50.0% by weight, more preferablyfrom 2.5 to 50.0% by weight, furthermore preferably from 5.0 to 40% byweight, and still furthermore preferably from 10.0 to 40.0% by weight,based on the weight of the binder composition. If the amount of curingaccelerator (b) is less than 0.5% by weight, the curing reaction ofbinder (a) is not accelerated sufficiently, and the initial strength ofthe resulting mold cannot be improved satisfactorily. If it exceeds63.0% by weight, the proportion of binder (a) becomes relatively small.It follows that curing accelerator (b) is not easily dissolved in binder(a), and sedimentation would occur in the binder composition.

The binder composition contains an acid-curable resin as binder (a),preferably in an amount of 40 to 99.5% by weight, more preferably from50 to 95% by weight and furthermore preferably 60 to 90% by weight,based on the weight of the binder composition. Any conventionalacid-curable resin may be used either individually or in combination oftwo or more thereof. Specific examples of useful acid-curable resininclude furfuryl alcohol, a furfuryl alcohol/aldehyde polycondensate, aphenol/aldehyde polycondensate, a melamine/aldehyde polycondensate, aurea/aldehyde polycondensate, and mixtures thereof. Co-condensationproducts of two or more of the above-mentioned polycondensates may alsobe used as an acid-curable resin.

The aldehyde to be polycondensed with the furfuryl alcohol, phenol,melamine or urea is conventional and examples thereof includeformaldehyde, glyoxal, and furfural. Among them, formaldehyde ispreferred in the present invention.

The weight average molecular weight of furfuryl alcohol/aldehydepolycondensate is preferably from 200 to 2,000, more preferably from 200to 1,500. When the weight average molecular weight is less than 200, thecuring rate of the binder is lowered, whereby the initial strength ofthe resulting mold tends to be lower. On the other hand, when the weightaverage molecular weight is higher than 2,000, the viscosity of thebinder composition increases, whereby the mulling characteristic of theresulting sand composition deteriorates, which may result in a decreasein the strength of the resulting mold.

The phenol to be polycondensed with an aldehyde is also conventional andexamples thereof include phenol, resorcinol, bisphenol A, bisphenol F, acompound represented by formula (2) shown below, a compound representedby formula (3) shown below, and mixtures of two or more thereof.##STR3## wherein R₁ represents a hydrocarbon group having from 1 to 10carbon atoms. ##STR4## wherein R₂ and R₃ each independently represent ahydrocarbon group having from 1 to 10 carbon atoms.

The phenol/aldehyde polycondensate is preferably the one prepared bycharging a phenolic monomer in a proportion of from 2 to 40% by weightbased on the total weight of the monomers. So, the unit derived from thephenolic monomer in the binder comprising the resulting phenol/aldehydepolycondensate is preferably from 2 to 40% by weight. If the phenolicmonomer unit content is less than 2% by weight, the curing rate becomesrelatively slow, tending to reduce the initial strength of the resultingmold. If it exceeds 40% by weight, the binder composition has anincreased viscosity which reduces the storage stability.

The weight average molecular weight of the phenol/aldehydepolycondensate is preferably from 200 to 3,000, more preferably from 200to 2,000. When the weight average molecular weight is less than 200, thecuring rate of the binder is lowered, whereby the initial strength ofthe resulting mold tends to be lower. On the other hand, when the weightaverage molecular weight is higher than 3,000, the viscosity of thebinder composition increases, whereby the mulling characteristic of theresulting sand composition deteriorates, which may result in a decreasein the resulting mold strength.

In using a urea/aldehyde polycondensate as an acid-curable resin, it ispreferable that urea bonded to an aldehyde be present in a givenproportion. That is, urea is preferably used in the binder compositionin such an amount that the nitrogen atom of urea origin may be presentin the binder composition in a proportion of from 0.1 to 6.0% by weight,and particularly from 0.1 to 4.5% by weight, based on the total weightof the binder composition. Use of the urea/aldehyde polycondensatehaving such an amount of nitrogen tends to improve the final strength ofthe resulting mold. If the urea is used in such an amount that thenitrogen content is less than 0.1% by weight, such a tendency to improvethe final strength is not shown any more. If the urea is used in such alarge amount that the nitrogen content exceeds 6.0% by weight, theresulting mold tends to have a disadvantage in that castings obtained byusing the casting mold often suffer from casting defect, such aspinholes. While the nitrogen content of urea origin has been referred towith respect to a urea/aldehyde polycondensate, the same preferrednitrogen content applies to other acid-curable resins. The nitrogencontent of the binder composition can be measured by the Kjeldahlmethod.

The weight average molecular weight of the urea/aldehyde polycondensateis preferably from 100 to 2,000, more preferably from 200 to 1,000. Ifthe weight average molecular weight is less than 100, the curing rate ofthe binder is low, whereby the initial strength of the resulting moldtends to be lower. On the other hand, if the weight average molecularweight is higher than 2,000, the viscosity of the binder compositionincreases, whereby the mulling characteristic of the resulting sandcomposition deteriorates, which may result in a decrease in the strengthof the resulting mold.

The weight average molecular weight of the melamine/aldehydepolycondensate is preferably from 200 to 2,000, more preferably from 200to 1,500. If the weight average molecular weight is less than 200, thecuring rate of the binder composition is low, whereby the initialstrength of the resulting mold tends to be lower. On the other hand, ifthe weight average molecular weight is higher than 2,000, the viscosityof the binder composition increases, whereby the mulling characteristicof the resulting sand composition deteriorates, which may result in adecrease in the strength of the resulting mold.

The binder composition of the present invention preferably has a watercontent of from 0.5 to 30.0% by weight, more preferably from 0.5 to10.0% by weight, based on the total weight of the binder composition.This water content serves to reduce the viscosity of the bindercomposition for easier handling. If the water content is less than 0.5%by weight, the decrease in the viscosity of the binder composition tendsto insufficient. A water content exceeding 30% by weight tends tointerfere with the curing reaction of the acid-curable resin, resultingin insufficient improvement in initial strength of the resulting mold.The water content of the binder composition can be determined by theKarl Fischer's method.

The binder composition can be prepared by mixing the acid-curable resin,such as furfuryl alcohol, and curing accelerator (b) comprising thecompound of formula (1). The acid-curable resin, such as furfurylalcohol, and the compound of formula (1) may be prepared simultaneouslyto give a binder composition comprising the acid-curable resin andcuring accelerator (b) consequently. The above-mentioned preferred watercontent may be supplied either by external addition of water or byproducing water simultaneously with the preparation of the acid-curableresin.

If desired, the binder composition of the present invention may furthercontain various known modifiers or additives in addition to components(a) and (b).

Mold making by the use of the aforesaid binder composition is generallycarried out as follows. A binder composition of the present inventionand a curing agent composition for curing the binder composition aremixed with a granular refractory material and mulling the resultingmixture to prepare a sand composition for mold making. The order ofaddition is not limited. For example, addition of the binder compositionmay be followed by addition of the curing agent composition, or viseversa, or the binder composition and the curing agent composition may beadded simultaneously. While not limiting, the binder composition and thecuring agent composition are generally added in an amounts of from about0.6 to 5 parts by weight (preferably from 0.6 to 3 parts by weight) andfrom about 0.2 to 3 parts by weight (preferably from 0.2 to 2 parts byweight), respectively, per 100 parts of the granular refractorymaterial. The curing agent composition to be added may previouslycontain conventional additives, for example, a known curing accelerator.

The granular refractory material which can be used in the presentinvention is conventional and examples thereof includes fresh orreclaimed sands, such as silica sand (mainly composed of quartz),chromite sand, zircon sand, olivine sand, alumina sand, mullite sand,and synthetic mullite sand. Reclaimed sands include those obtained bymechanical reclamation or thermal reclamation. Mechanical reclamationachieves a high yield and is economically advantageous and customary,and thus is preferred. Such reclaimed sand is preferably used in thepresent invention.

The curing agent composition which can be used in combination with thebinder composition of the present invention includes a conventionalphosphorus-containing compound (e.g., phosphoric acid, condensedphosphoric acid, phosphoric esters (methyl phosphate) and phosphates(calcium phosphate or potassium hydrogenphosphate)), a conventionalsulfur-containing compound (e.g., a sulfonic acid compound(methanesulfonic acid, ethanesulfonic acid, phenolsulfonic acid,benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, etc.)and sulfuric acid), and a mixture of two or more thereof. In particular,a phosphorus-containing compound or a mixture thereof is preferred. Ascompared with a sulfur-containing curing agent composition,phosphorus-containing curing agent compositions have lower acid strengthand therefore a lower curing rate but, on the other hand, produce lesspoisonous gas on pouring a casting material and therefore are favorablefor the working environment. Although it has a lower curing rate, itgives rise to no great problem by virtue of the improvement in curingrate of the binder composition of the present invention per se.

If yet a further improvement in curing rate being desired, it isrecommended to use a phosphorus-containing compound excellent in theworking environment in combination with a sulfur-containing compoundhaving a high acid strength and capable of accelerating curing. Thecuring agent system comprising a phosphorus-containing compound and asulfur-containing compound will hereinafter be referred to as a curingagent composition.

Examples of the phosphorus-containing compound which can be used in thecuring agent composition of the present invention includes phosphoricacid, condensed phosphoric acid, a phosphoric ester (e.g., methylphosphate or ethyl phosphate) and a phosphate (e.g., calcium phosphateor potassium hydrogenphosphate) and mixtures thereof. Examples of thesulfur-containing compound which can be used in the curing agentcomposition of the present invention includes sulfuric acid,methanesulfonic acid, ethanesulfonic acid, phenolsulfonic acid,benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, andmixtures thereof.

In the curing agent composition, the phosphorus-containing compound andthe sulfur-containing compound are preferably present at such a ratiothat the weight ratio of sulfur atoms to the total weight of phosphorusatoms and sulfur atoms is from 0.01 to 0.7. In other words, the weightof sulfur atoms is preferably from 1/99 to 7/3 of the weight ofphosphorus atoms. If the sulfur content is less than this range, meaningthat the phosphorus content is higher than the range, phosphorus isliable to accumulate in reclaimed sand in a large quantity, resulting incasting defects, such as pinholes. In addition, the sand willconsiderably absorb moisture due to the accumulated phosphorus, leadingto interfere the curing of the acid-curable resin. If the sulfur contentis more than that range, too large an amount of the sulfur-containingcompound is liable to result in the release of poisonous decompositionproducts upon pouring of a casting material, resulting in deteriorationof the working environment. It is particularly preferred to adjust theweight ratio of sulfur atoms to the total weight of phosphorus atoms andsulfur atoms within a range of from 0.03 to 0.6.

For the purpose of further improving mold strength, a silane couplingagent may be added to the granular refractory material. Examples of thesilane coupling agents include(2-amino)aminopropylmethyldimethoxysilane,γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, andγ-glycidoxypropyltrimethoxysilane. The silane coupling agent maypreviously be incorporated into the binder composition.

The thus prepared sand composition for mold making (hereinafter simplyreferred to as a sand composition) can generally be used for productionof molds by self-hardening casting mold making. That is, the sandcomposition is charged in a prescribed pattern, and the bindercomposition is allowed to cure by the action of the curing agent toobtain a mold. The binder composition of the present invention exhibitsa relatively high curing rate so that it takes only about 30 minutes to1 hour from pattern filling to removal from the pattern. Castings ofhigh quality can be produced by pouring a casting material into the thusobtained casting mold. Neither heating nor cooling is needed in mixingof materials, molding, or curing, and all these steps may be conductedat ambient temperature.

The present invention will now be illustrated in greater detail withreference to Examples, but it should be understood that the presentinvention is not construed as being limited thereto. All the parts andpercents are given by weight unless otherwise indicated.

EXAMPLES Examples 1 to 12 and Comparative Examples 1 to 3

Furfuryl alcohol (acid-curable resin) was mixed with a curingaccelerator shown in Table 1 below (e.g., 2,5-bishydroxymethylfuran("2,5-Furandimethanol" produced by Aldrich Fine Chemical Co.; CASregistration number: 1883-75-6)) in an amount shown in Table 1 toprepare a binder composition. To 100 parts of silica sand ("KaketsuFusen No. 5") were added 1 part of the binder composition and 0.45 partof a curing agent (a 70% aqueous solution of toluenesulfonic acid), andthe mixture was mulled to obtain a sand composition.

The resulting sand composition was charged in a test piece frame of 50mm in diameter and 50 mm in height at 25° C. and maintained for 1 houror 24 hours. The compressive strength of the thus obtained mold wasmeasured in accordance with JIS Z 2604-1976 (the term "JIS" means"Japanese Industrial Standard"). The results obtained are shown in Table1 below.

                  TABLE 1                                                         ______________________________________                                                            Compressive Strength                                             Curing Accelerator                                                                           After     After                                         Example              Amount   1 Hr.   24 Hrs.                                 No.      Kind        (wt %)   (kg/cm.sup.2)                                                                         (kg/cm.sup.2)                           ______________________________________                                        Example 1                                                                              bishydroxy- 0.5      5.1     32.8                                             methylfuran                                                          Example 2                                                                              bishydroxy- 2.5      7.3     33.5                                             methylfuran                                                          Example 3                                                                              bishydroxy- 5.0      8.8     34.5                                             methylfuran                                                          Example 4                                                                              bishydroxy- 7.5      10.2    36.5                                             methylfuran                                                          Example 5                                                                              bishydroxy- 10.0     11.4    38.0                                             methylfuran                                                          Example 6                                                                              bishydroxy- 20.0     17.7    42.5                                             methylfuran                                                          Example 7                                                                              bishydroxy- 300      24.8    48.3                                             methylfuran                                                          Example 8                                                                              bishydroxy- 400      28.1    52.6                                             methylfuran                                                          Example 9                                                                              bishydroxy- 500      26.8    51.2                                             methylfuran                                                          Example 10                                                                             bishydroxy- 60.0     25.6    46.8                                             methylfuran                                                          Example 11                                                                             bishydroxy- 20.0                                                              methylfuran +        18.1    43.2                                             bismethoxy- 1.5                                                               methylfuran                                                          Example 12                                                                             bishydroxy- 15.0                                                              methylfuran +        15.5    40.0                                             bismethoxy- 1.0                                                               methylfuran                                                          Comparative                                                                            bishydroxy- 0.3      3.2     29.8                                    Example 1                                                                              methylfuran                                                          Comparative                                                                            none        --       3.2     29.4                                    Example 2                                                                     Comparative                                                                            bishydroxy- 65.0     unmeasurable due                                Example 3                                                                              methylfuran          to non-uniformity                               ______________________________________                                    

As is apparent from the results in Table 1, when the binder compositioncontaining the curing accelerator of the present invention is used, themold strength after 1 hour increases, and that after 24 hours alsoincreases. As the content of the curing accelerator is graduallyincreased from 0.5% by weight, the strength of the mold also graduallyincreases, reaching the maximum at 50% by weight. As the curingaccelerator content is further increased, the mold strength graduallydecreases. If the curing accelerator content exceeds 65% by weight, thebinder composition becomes non-uniform. At a curing accelerator contentbelow 0.5% by weight, the improvement in mold strength is not so great.

Examples 13 to 24 and Comparative Examples 4 to 6

A test piece was prepared in the same manner as in Examples 1 to 12,except for using an equivalent weight mixture of a 70% aqueous solutionof toluenesulfonic acid and a 85% aqueous solution of phosphoric acid asa curing agent composition. The compressive strengths of the resultingtest pieces measured in the same manner as in Example 1 are shown inTable 2 below.

                  TABLE 2                                                         ______________________________________                                                            Compressive Strength                                             Curing Accelerator                                                                           After     After                                         Example              Amount   1 Hr.   24 Hrs.                                 No.      Kind        (wt %)   (kg/cm.sup.2)                                                                         (kg/cm.sup.2)                           ______________________________________                                        Example 13                                                                             bishydroxy- 0.5      5.4     33.5                                             methylfuran                                                          Example 14                                                                             bishydroxy- 2.5      7.7     34.2                                             methylfuran                                                          Example 15                                                                             bishydroxy- 5.0      9.2     35.1                                             methylfuran                                                          Example 16                                                                             bishydroxy- 7.5      10.6    37.3                                             methylfuran                                                          Example 17                                                                             bishydroxy- 10.0     11.9    38.6                                             methylfuran                                                          Example 18                                                                             bishydroxy- 20.0     18.1    43.3                                             methylfuran                                                          Example 19                                                                             bishydroxy- 30.0     25.5    49.1                                             methylfuran                                                          Example 20                                                                             bishydroxy- 40.0     29.0    53.0                                             methylfuran                                                          Example 21                                                                             bishydroxy- 50.0     27.2    52.0                                             methylfuran                                                          Example 22                                                                             bishydroxy- 60.0     25.8    47.4                                             methylfuran                                                          Example 23                                                                             bishydroxy- 20.0                                                              methylfuran +        18.4    43.7                                             bismethoxy- 1.5                                                               methylfuran                                                          Example 24                                                                             bishydroxy- 15.0                                                              methylfuran +        16.0    40.6                                             bismethoxy- 1.0                                                               methylfuran                                                          Comparative                                                                            bishydroxy- 0.3      3.3     30.4                                    Example 4                                                                              methylfuran                                                          Comparative                                                                            none        --       3.0     30.1                                    Example 5                                                                     Comparative                                                                            bishydroxy- 65.0     unmeasurable due to                             Example 6                                                                              methylfuran          non-uniformity                                  ______________________________________                                    

As can be seen from Table 2, when the binder composition containing thecuring accelerator of the present invention is used, the mold strengthafter 1 hour increases, and that after 24 hours also increases. As thecontent of the curing accelerator is gradually increased from 0.5% byweight, the strength of the mold also gradually increases, reaching themaximum at 40% by weight. As the curing accelerator content is furtherincreased, the mold strength gradually decreases. When the curingaccelerator content exceeds 65% by weight, the binder compositionbecomes non-uniform. At a curing accelerator content below 0.5% byweight, the improvement in mold strength is not so great.

PREPARATION OF BINDER COMPOSITIONS 1-15

Furfuryl alcohol or a mixture of furfuryl alcohol and an acid-curableresin selected from a furfuryl alcohol/aldehyde polycondensate, aphenol/aldehyde polycondensate, a melamine/aldehyde polycondensate and aurea/aldehyde polycondensate was prepared as a binder. Bindercompositions 1 to 15 were prepared using the binder and other componentsas shown in Table 3 below. In the Table, the amounts of the binder,water, curing accelerator and other component are given by % by weightbased on the total weight of the composition. The nitrogen content isgiven in terms of % by weight of nitrogen atoms based on the total atomsin the composition.

The binders, such as a furfuryl alcohol/aldehyde polycondensate, wereprepared as follows.

Preparation of Furfuryl Alcohol/Aldehyde Polycondensate:

Furfuryl alcohol and aldehyde were reacted under an acidic condition fora prescribed period of time in a conventional manner to prepare afurfuryl alcohol/aldehyde polycondensate.

Preparation of Phenol/Aldehyde Polycondensate:

Phenol and an aldehyde were reacted under a basic condition for aprescribed period of time in a conventional manner. After completion ofthe reaction, the reaction mixture was neutralized with ap-toluenesulfonic acid aqueous solution to obtain a phenol/aldehydepolycondensate.

Preparation of Melamine/Aldehyde Polycondensate:

Melamine and aldehyde were reacted under a basic condition for aprescribed period of time in a conventional manner. After completion ofthe reaction, the reaction mixture was neutralized with ap-toluenesulfonic acid aqueous solution to obtain a melamine/aldehydepolycondensate.

Preparation of Urea/Aldehyde Polycondensate:

Urea and an aldehyde were reacted under a basic condition for aprescribed period of time in a conventional manner. After completion ofthe reaction, the reaction mixture was neutralized with ap-toluenesulfonic acid aqueous solution to obtain a urea/aldehydepolycondensate.

In the present invention including the Examples and Comparative Examplesherein, each characteristic was measured in the following manner.

Content (ratio) of Furfuryl Alcohol and Compound of Formula (1), e.g.,2,5-bishydroxymethylfuran:

It was measured by gas chromatography under the following conditions:

    ______________________________________                                        Chromatograph:                                                                              GC-14A, manufactured by Shimadzu                                              Corporation                                                     Column:       PEG-20M chromosorb WAW DMCS                                                   10% 60/80 mesh; 0.5 m × 3 mm .0.                          Detector:     FID                                                             Carrier gas:  He                                                              ______________________________________                                    

Water Content:

It was measured by Karl Fischer's method.

Content of Phenolic Monomer Unit (e.g., phenol) in terms of Amount ofRaw monomer:

It was measured with an ultraviolet spectrophotometer.

Nitrogen content:

It was measured by the Kjeldahl method.

                                      TABLE 3                                     __________________________________________________________________________    Component (wt %)  1  2  3  4  5  6  7  8                                      __________________________________________________________________________    Binder:                                                                       Furfuryl alcohol  57.5                                                                             50.3                                                                             61.7                                                                             84.4                                                                             35.8                                                                             35.5                                                                             43.6                                                                             56.7                                   Furfuryl alcohol/formaldehyde                                                                   22.0                                                                             15.7                                                                             8.2                                                                              3.7                                                                              14.5                                                                             12.4                                                                             18.9                                                                             6.6                                    polycondensate                                                                Urea/formaldehyde polycondensate                                                                -- 12.9                                                                             12.5                                                                             5.5                                                                              20.1                                                                             14.3                                                                             1.6                                                                              11.9                                   Phenol/formaldehyde polycondensate                                                              -- -- -- -- -- -- -- 8.1                                    Melamine/formaldehyde polycon-                                                                  -- -- -- -- -- -- -- --                                     densate                                                                       Phenol/furfural polycondensate                                                                  -- -- -- -- -- -- -- --                                     Urea/glyoxal polycondensate                                                                     -- -- -- -- -- -- -- --                                     Water Content     5.0                                                                              6.0                                                                              4.0                                                                              1.4                                                                              6.2                                                                              12.6                                                                             0.7                                                                              4.2                                    Bishydroxymethylfuran (curing                                                                   15.5                                                                             15.1                                                                             13.6                                                                             5.0                                                                              23.4                                                                             25.2                                                                             35.2                                                                             12.5                                   accelerator)                                                                  Nitrogen Content  -- 2.5                                                                              2.5                                                                              0.9                                                                              3.8                                                                              3.0                                                                              0.3                                                                              2.3                                    Other Component                                                               Phenol Content    -- -- -- -- -- -- -- 4.5                                    (in terms of amount of raw monomer)                                           __________________________________________________________________________    Component (wt %)  9  10 11 12 13 14 15                                        __________________________________________________________________________    Binder:                                                                       Furfuryl alcohol  53.0                                                                             46.8                                                                             58.9                                                                             59.4                                                                             100.0                                                                            74.7                                                                             74.8                                      Furfuryl alcohol/formaldehyde                                                                   10.2                                                                             -- 10.6                                                                             -- -- 18.8                                                                             --                                        polycondensate                                                                Urea/formaldehyde polycondensate                                                                12.2                                                                             8.2                                                                              -- -- -- -- 17.2                                      Phenol/formaldehyde polycondensate                                                              -- -- -- -- -- -- --                                        Melamine/formaldehyde polycon-                                                                  3.0                                                                              -- -- -- -- -- --                                        densate                                                                       Phenol/furfural polycondensate                                                                  -- -- 9.1                                                                              -- -- -- --                                        Urea/glyoxal polycondensate                                                                     -- -- -- 6.0                                                                              -- -- --                                        Water Content     3.8                                                                              2.2                                                                              3.8                                                                              2.3                                                                              0.0                                                                              6.2                                                                              8.0                                       Bishydroxymethylfuran (curing                                                                   17.8                                                                             42.8                                                                             17.6                                                                             32.3                                                                             -- 0.3                                                                              --                                        accelerator)                                                                  Nitrogen Content  2.5                                                                              0.7                                                                              -- 0.5                                                                              -- -- 3.6                                       Phenol monomer (other                                                                           -- -- 4.5                                                                              -- -- -- --                                        component)                                                                    __________________________________________________________________________

Examples 25 to 36 and Comparative Examples 7 to 9

A test piece was prepared in the same manner as in Examples 1 to 13,except for using each of binder compositions 1 to 15. The compressivestrength of the resulting test piece is shown in Table 4 below.

                  TABLE 4                                                         ______________________________________                                                        Compressive Strength                                          Example   Binder      After 1 Hr. After 24 Hrs.                               No.       Composition (kg/cm.sup.2)                                                                             (kg/cm.sup.2)                               ______________________________________                                        Example 25                                                                              1           13.8        35.8                                        Example 26                                                                              2           13.2        37.7                                        Example 27                                                                              3           12.8        40.2                                        Example 28                                                                              4           8.5         36.0                                        Example 29                                                                              5           13.2        37.0                                        Example 30                                                                              6           9.2         36.6                                        Example 31                                                                              7           18.7        35.2                                        Example 32                                                                              8           13.0        38.7                                        Example 33                                                                              9           15.4        38.2                                        Example 34                                                                              10          25.1        48.7                                        Example 35                                                                              11          14.7        38.0                                        Example 36                                                                              12          24.8        47.2                                        Comparative                                                                             13          3.0         29.4                                        Example 7                                                                     Comparative                                                                             14          3.3         27.8                                        Example 8                                                                     Comparative                                                                             15          3.5         30.2                                        Example 9                                                                     ______________________________________                                    

As can be seen from Table 4, when the binder composition containing aprescribed amount of 2,5-bishydroxymethylfuran is used, the resultingmold has a relatively high initial strength and a satisfactory strengthafter 24 hours, though showing some scatter depending on the kind of thebinder. To the contrary, when using the binder composition containing noor an extremely small amount of 2,5-bishydroxymethylfuran, the mold hasa low strength either in the initial stage or after 24 hours,irrespective of the kind of the binder.

Examples 37 to 48 and Comparative Example 10

A binder composition was prepared by adding the curing accelerator shownin Table 5 below to a furfuryl alcohol/formaldehyde polycondensatecontaining 0.3% by weight of bishydroxymethylfuran in an amount shown inTable 5. A test piece was obtained in the same manner as in Examples 1to 12, except for using the thus prepared binder composition. Thecompressire strengths of the resulting test pieces are shown in Table 5.

                  TABLE 5                                                         ______________________________________                                                            Compressive Strength                                             Curing Accelerator                                                                           After     After                                         Example              Amount   1 Hr.   24 Hrs.                                 No.      Kind        (wt %)   (kg/cm.sup.2)                                                                         (kg/cm.sup.2)                           ______________________________________                                        Example 37                                                                             bishydroxy- 0.5      5.3     29.6                                             methylfuran                                                          Example 38                                                                             bishydroxy- 2.5      7.8     30.2                                             methylfuran                                                          Example 39                                                                             bishydroxy- 5.0      9.2     31.1                                             methylfuran                                                          Example 40                                                                             bishydroxy- 7.5      10.4    32.9                                             methylfuran                                                          Example 41                                                                             bishydroxy- 10.2     11.7    34.3                                             methylfuran                                                          Example 42                                                                             bishydroxy- 21.7     18.0    38.3                                             methylfuran                                                          Example 43                                                                             bishydroxy- 32.5     25.3    43.5                                             methylfuran                                                          Example 44                                                                             bishydroxy- 41.8     28.4    47.4                                             methylfuran                                                          Example 45                                                                             bishydroxy- 50.3     27.1    46.2                                             methylfuran                                                          Example 46                                                                             bishydroxy- 62.1     25.9    42.2                                             methylfuran                                                          Example 47                                                                             bishydroxy- 22.4                                                              methylfuran +        18.3    38.9                                             bismethoxy- 1.5                                                               methylfuran                                                          Example 48                                                                             bishydroxy- 15.0                                                              methylfuran +        15.7    36.1                                             bismethoxy- 1.0                                                               methylfuran                                                          Comparative                                                                            bishydroxy- 0.3      3.4     26.9                                    Example 10                                                                             methylfuran                                                          ______________________________________                                    

As can be seen from the results in Table 5, when the binder compositioncontaining the curing accelerator of the present invention is used, theresulting mold has an increased strength both after 1 hour and after 24hours. As the content of the curing accelerator is gradually increasedfrom 0.5% by weight, the strength of the mold also gradually increases,reaching the maximum at about 40% by weight. As the curing acceleratorcontent is further increases, the mold strength gradually decreases. Atthe curing accelerator content below 0.5% by weight, the improvement inmold strength is not so great.

Examples 49 to 60 and Comparative Examples 11 to 13

A test piece was prepared in the same manner as in Examples 1 to 12,except for using a 85% by weight phosphoric acid aqueous solution as acuring agent. Differing from Examples 1 to 12, the compressive strengthsof the resulting sample molds after an elapse of 2 hours and 24 hourswere measured in these Examples and Comparative Examples. The resultsobtained are shown in Table 6.

                  TABLE 6                                                         ______________________________________                                                            Compressive Strength                                             Curing Accelerator                                                                           After     After                                         Example              Amount   2 Hr.   24 Hrs.                                 No.      Kind        (wt %)   (kg/cm.sup.2)                                                                         (kg/cm.sup.2)                           ______________________________________                                        Example 49                                                                             bishydroxy- 0.5      4.2     32.1                                             methylfuran                                                          Example 50                                                                             bishydroxy- 2.5      6.0     32.8                                             methylfuran                                                          Example 51                                                                             bishydroxy- 5.0      7.2     33.8                                             methylfuran                                                          Example 52                                                                             bishydroxy- 7.5      8.3     35.8                                             methylfuran                                                          Example 53                                                                             bishydroxy- 10.0     9.3     37.2                                             methylfuran                                                          Example 54                                                                             bishydroxy- 20.0     14.5    41.7                                             methylfuran                                                          Example 55                                                                             bishydroxy- 30.0     20.3    47.3                                             methylfuran                                                          Example 56                                                                             bishydroxy- 40.0     23.0    51.5                                             methylfuran                                                          Example 57                                                                             bishydroxy- 50.0     21.9    50.2                                             methylfuran                                                          Example 58                                                                             bishydroxy- 60.0     20.9    45.9                                             methylfuran                                                          Example 59                                                                             bishydroxy- 20.0                                                              methylfuran +        14.8    42.3                                             bismethoxy- 1.5                                                               methylfuran                                                          Example 60                                                                             bishydroxy- 15.0                                                              methylfuran +        12.7    39.2                                             bismethoxy- 1.0                                                               methylfuran                                                          Comparative                                                                            bishydroxy- 0.3      2.6     29.2                                    Example 11                                                                             methylfuran                                                          Comparative                                                                            bishydroxy- 0        2.5     28.8                                    Example 12                                                                             methylfuran                                                          Comparative                                                                            bishydroxy- 65.0     unmeasurable due to                             Example 13                                                                             methylfuran          non-uniformity                                  ______________________________________                                    

As is apparent from Table 6, when the binder composition containing thecuring accelerator of the present invention is used, the resultingsample mold has an increased strength either after 2 hours or 24 hours.As the content of the curing accelerator is gradually increased from0.5% by weight, the strength of the mold also gradually increases,reaching the maximum at 40% by weight. As the curing accelerator contentis further increased, the mold strength gradually decreases. When thecuring accelerator content exceeds 65% by weight, the binder compositionbecomes non-uniform. At a curing accelerator content below 0.5% byweight, the improvement in mold strength is not so great. It is alsoseen that use of phosphoric acid as a curing agent causes a reduction ininitial mold strength (strength after an elapse of 1 to 2 hours) ascompared with use of toluenesulfonic acid.

Examples 61 to 65 and Comparative Examples 14 and 15

A binder composition shown in Table 7 below was prepared from a bindercomprising furfuryl alcohol, a furfuryl alcohol/formaldehydepolycondensate, and a urea/formaldehyde polycondensate and a curingaccelerator. A hundred parts of furan reclaimed sand were mixed andmulled with 0.8 part of the thus prepared binder composition and 0.4part of a curing agent (60% aqueous solution of xylenesulfonic acid) toprepare a sand composition for mold making. Test pieces were prepared inthe same manner as in Examples 1 to 12 using the sand composition. Thecompressive strengths of the test pieces are shown in Table 7.

                                      TABLE 7                                     __________________________________________________________________________           Binder Composition for Mold Making                                            Binder                 Curing      Compressive                                     Furfuryl Alcohol/                                                                       Urea/Form/                                                                            Accelerator Strength                                   Furfuryl                                                                           Formaldehyde                                                                            aldehyde                                                                              Bishydroxy-                                                                          Water                                                                              After                                                                              After                          Example                                                                              Alcohol                                                                            Polycondensate                                                                          Polycondensate                                                                        methylfuran                                                                          Content                                                                            1 Hr.                                                                              24 Hrs.                        No.    (wt %)                                                                             (wt %)    (wt %)  (wt %) (wt %)                                                                             (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                  __________________________________________________________________________    Example 61                                                                           55.6 5.9       17.5     5.0   16.0 11.8 42.0                           Example 62                                                                           46.5 5.9       17.6    10.0   20.0 10.2 40.1                           Example 63                                                                           39.7 2.7       18.6    15.0   24.0 10.7 38.5                           Example 64                                                                           42.1 2.7       16.2    15.0   24.0 10.9 37.8                           Example 65                                                                           35.8 2.8       16.4    17.0   28.0  8.8 34.2                           Comparative                                                                          56.5 5.9       17.6     0.0   20.0  3.2 37.3                           Example 14                                                                    Comparative                                                                          52.8 2.8       16.4     0.0   28.0  0.8 31.6                           Example 15                                                                    __________________________________________________________________________

As is apparent from Table 7, when the binder composition containing thecuring accelerator of the present invention is used, the resulting moldhas an increased strength either after 1 hour or after 24 hours.

Examples 66 to 77 and Comparative Examples 16 to 18

A curing agent composition containing 11.3% of sulfuric acid and 38.8%of phosphorus pentoxide was prepared. The [sulfur/(phosphorus+sulfur)]weight ratio was found to be 0.178. Separately, furfuryl alcohol(acid-curable resin) was mixed with a curing accelerator, e.g.,2,5-bishydroxymethylfuran ("2,5-Furandimethanol" produced by AldrichFine Chemical Co.; CAS registration number: 1883-75-6) in the amountshown in Table 8 below to prepare a binder composition. To 100 parts ofsilica sand was added 0.33 part of the curing agent composition, andthen 0.65 part of the binder composition was added thereto and theresulting mixture was mulled to obtain a sand composition. The sandcomposition was molded into a mold, and a casting was obtained using theresulting mold at a mold/molten metal weight ratio of 2.5. Thereafter,the mold was broken, and the recovered sand was crushed in a crusher andreclaimed in an M type rotary reclaimer manufactured by Nippon ChuzoCo., Ltd. to obtain reclaimed sand.

Ninety-five parts of the reclaimed sand and 5 parts of new sand weremixed, and the same amounts of the same curing agent composition andbinder composition as used above were added thereto to prepare a sandcomposition. The cycle consisting of mold making, casting, recovery, andreclamation was repeated 20 times. The sulfur dioxide (SO₂)concentration in the working environment was measured at the time ofcasting of the 20th cycle.

A sand composition prepared in the same manner as described above byusing the 20-times reclaimed sand was charged in a pattern for moldmaking, and the compressive strength of the resulting mold after anelapse of 0.5 hour, 1 hour and 24 hours from the charging was measured.The results obtained are shown in Table 8.

                  TABLE 8                                                         ______________________________________                                                           Compressive Strength                                                            After   After   After                                    Curing Accelerator   0.5 Hr  1.0 Hr  24 Hrs                                   Example             Amount   (kg/  (kg/  (kg/                                 No.     Kind        (wt %)   cm.sup.2)                                                                           cm.sup.2)                                                                           cm.sup.2)                            ______________________________________                                        Example 66                                                                            bishydroxy- 0.5      1.5   5.3   32.8                                         methylfuran                                                           Example 67                                                                            bishydroxy- 2.5      2.2   7.6   33.9                                         methylfuran                                                           Example 68                                                                            bishydroxy- 5.0      3.8   9.0   34.7                                         methylfuran                                                           Example 69                                                                            bishydroxy- 7.5      4.5   9.8   37.0                                         methylfuran                                                           Example 70                                                                            bishydroxy- 10.0     4.9   10.6  38.5                                         methylfuran                                                           Example 71                                                                            bishydroxy- 20.0     6.2   16.8  43.1                                         methylfuran                                                           Example 72                                                                            bishydroxy- 30.0     7.0   23.7  48.6                                         methylfuran                                                           Example 73                                                                            bishydroxy- 40.0     9.3   27.6  52.3                                         methylfuran                                                           Example 74                                                                            bishydroxy- 50.0     7.1   25.3  50.2                                         methylfuran                                                           Example 75                                                                            bishydroxy- 60.0     6.8   23.2  46.8                                         methylfuran                                                           Example 76                                                                            bishydroxy- 20.0                                                              methylfuran +        5.7   16.5  43.1                                         bismethoxy- 1.0                                                               methylfuran                                                           Example 77                                                                            bishydroxy- 15.0                                                              methylfuran +        5.0   15.2  40.0                                         bismethoxy- 1.0                                                               methylfuran                                                           Com-    bishydroxy- 0.3      0     2.8   30.2                                 parative                                                                              methylfuran                                                           Example 16                                                                    Com-    --          --       0     2.5   29.8                                 parative                                                                      Example 17                                                                    Com-    bishydroxy- 65.0     unmeasurable due to                              parative                                                                              methylfuran          non-uniformity                                   Example 18                                                                    ______________________________________                                    

As is apparent from Table 8, when the binder composition containing thecuring accelerator of the present invention is used, the resultingsample mold has an increased strength either after 0.5 hour, 1 hour or24 hours. As the content of the curing accelerator is graduallyincreased from 0.5% by weight, the strength of the mold also graduallyincreases, reaching the maximum at 40% by weight. As the curingaccelerator content is further increased, the mold strength graduallydecreases. When the curing accelerator content exceeds 65% by weight,the binder composition becomes non-uniform. At the curing acceleratorcontent below 0.5% by weight, the improvement in mold strength is not sogreat.

Examples 78 to 83 and Reference Examples 1 and 2

Curing agent compositions were prepared from a sulfur-containingcompound and P₂ O₅ as a phosphorus-containing compound as shown in Table9 below. In Table 9, the balance the sulfur-containing compound and thephosphorus-containing compound was water. The sulfur content, phosphoruscontent, and the weight ratio of sulfur to (sulfur+phosphorus) of thecuring agent compositions are also shown in Table 9.

                                      TABLE 9                                     __________________________________________________________________________    Curing Agent Composition                                                      S-Containing Compound Amount                                                                             S    P                                             Example          Amount                                                                             of P.sub.2 O.sub.5                                                                 Content                                                                            Content                                       No.   Kind       (wt %)                                                                             (wt %)                                                                             (wt %)                                                                             (wt %)                                                                             S/(S + P)                                __________________________________________________________________________    Example 78                                                                          Methanesulfonic acid                                                                     2.7  15.3 13.95                                                                              6.7  0.676                                          Toluenesulfonic acid                                                                     35.0                                                               Sulfuric acid                                                                            20.0                                                         Example 79                                                                          Ethanesulfonic acid                                                                      2.0  15.3 3.9  6.7  0.368                                          Phenolsulfonic acid                                                                      14.5                                                               Benzenesulfonic acid                                                                     3.2                                                          Example 80                                                                          Phenolsulfonic acid                                                                      6.8  30.7 9.25 13.4 0.408                                          Toluenesulfonic acid                                                                     38.6                                                               Xylenesulfonic acid                                                                      4.8                                                          Example 81                                                                          Xylenesulfonic acid                                                                      8.5  30.7 2.9  13.4 0.178                                          Phenolsulfonic acid                                                                      7.8                                                          Example 82                                                                          Benzenesulfonic acid                                                                     19.5 42.4 5.8  18.5 0.239                                          Sulfuric acid                                                                            7.5                                                          Example 83                                                                          Benzenesulfonic acid                                                                     1.0  36.6 0.6  16.0 0.036                                          Toluenesulfonic acid                                                                     2.1                                                          Reference                                                                           Toluenesulfonic acid                                                                     0.5  39.9 0.12 17.42                                                                              0.007                                    Example 1                                                                           Sulfuric acid                                                                            0.1                                                          Reference                                                                           Benzenesulfonic acid                                                                     48.5 6.1  16.74                                                                              2.68 0.862                                    Example 2                                                                           Toluenesulfonic acid                                                                     5.2                                                                Sulfuric acid                                                                            18.2                                                         __________________________________________________________________________

Separately, a binder composition comprising a furan resin (acid-curableresin) having a nitrogen content of 2.5% by weight and 15.0% by weightof bishydroxymethylfuran as a curing accelerator was prepared.

Mold making and reclamation of sand were repeatedly carried out in thesame manner as in Examples 66 to 77, except for using each of the curingagent compositions of Table 9, and the compressive strength of thefinally obtained mold were evaluated at 5° C. and 35° C. in the samemanner as in Examples 66 to 77. The moisture absorption of the reclaimedsand was also determined by allowing the 20-times reclaimed sand tostand at 25° C. under an environment of 90% RH for 24 hours and thenmeasuring the amount of the moisture absorbed to the sand. Further, SO₂generation quantity at the 20-times mold making was measured under asevere condition, as follows.

Measurement of SO₂ Generation Quantity:

Immediately after pouring a casting material into a mold having a sizeof 620 mm×770 mm×530 mmh and the mold/molten metal weight ratio of 2.5,the mold was covered by a wooden box having a size of 900 mm×900 mm×900mmh and the SO₂ concentration was measured by a sensor tube located atthe top of the wooden box at 5 minutes after the completion of casting.

The results obtained are shown in Table 10 below.

                  TABLE 10                                                        ______________________________________                                                         Compressive Strength                                                          (kg/cm.sup.2)                                                        Moisture SO.sub.2                 Measur-                                     Absorp-  Generation               ing                                 Example tion     Quantity  0.5  1.0  24   Temp.                               No.     (%*)     (ppm)     Hr   Hr   Hrs  (°C.)                        ______________________________________                                        Example 78                                                                            0.21     72.0      3.0  8.9  40.2  5                                  Example 79                                                                            0.25     21.0      4.8  9.2  39.3 35                                  Example 80                                                                            0.23     47.8      3.2  8.3  40.9  5                                  Example 81                                                                            0.27     16.0      5.2  9.9  37.1 35                                  Example 82                                                                            0.26     28.0      4.9  9.8  39.5  5                                  Example 83                                                                            0.28      3.5      5.2  9.1  38.1 35                                  Reference                                                                             0.45      1.5      0    0.6  11.5 35                                  Example 1                                                                     Reference                                                                             0.18     95.0      2.1  8.0  37.3  5                                  Example 2                                                                     ______________________________________                                         Note:                                                                         *Based on the sand                                                       

Tables 9 and 10 reveal that the reclaimed sand has a high moistureabsorption and the resulting mold has a reduced compressive strengthwhen the S/(S+P) weight ratio in the curing agent composition is lessthan 0.01. It is also proved that the working environment is seriouslydeteriorated if the S/(S+P) weight ratio exceeds 0.7.

On the other hand, when the curing agent compositions of Examples 78 to83 are used, the moisture absorption of the reclaimed sand is small, theresulting mold has an increased strength, and also the workingenvironment is satisfactory.

Examples 84 to 95 and Comparative Examples 19 to 21

Test pieces were prepared in the same manner as in Examples 78 to 83using each of the binder compositions 1 to 15 and the curing agentcomposition used in Examples 78 to 83. The compressive strengths of theresulting test pieces are shown in Table 11 below.

                  TABLE 11                                                        ______________________________________                                                      Compressive Strength                                            Example  Binder     0.5 Hr    1 Hr   24 Hrs                                   No.      Composition                                                                              (kg/cm.sup.2)                                                                           (kg/cm.sup.2)                                                                        (kg/cm.sup.2)                            ______________________________________                                        Example 84                                                                             1          4.8       11.3   34.4                                     Example 85                                                                             2          4.5       10.8   36.2                                     Example 86                                                                             3          4.2       10.5   36.8                                     Example 87                                                                             4          3.8       7.0    34.6                                     Example 88                                                                             5          4.3       10.8   35.5                                     Example 89                                                                             6          4.0       7.5    35.1                                     Example 90                                                                             7          5.8       15.3   33.8                                     Example 91                                                                             8          4.5       10.6   37.1                                     Example 92                                                                             9          5.1       12.7   36.7                                     Example 93                                                                             10         6.5       19.8   46.5                                     Example 94                                                                             11         4.8       12.1   36.5                                     Example 95                                                                             12         6.4       19.6   45.3                                     Comparative                                                                            13         0         3.0    28.2                                     Example 19                                                                    Comparative                                                                            14         0         3.3    26.7                                     Example 20                                                                    Comparative                                                                            15         0         3.5    29.0                                     Example 21                                                                    ______________________________________                                    

As can be seen from Table 11, when the binder composition containing aprescribed amount of 2,5-bishydroxymethylfuran is used, the resultingmold has a relatively high initial strength and a satisfactory strengthafter 24 hours, though showing some scatter depending on theacid-curable resin used as a binder. To the contrary, in using thebinder composition containing no or an extremely small amount of2,5-bishydroxymethylfuran, the mold has a low strength either in theinitial stage or after 24 hours, irrespective of the kind of the binder.

The binder composition in accordance with the present invention containsa prescribed amount of the compound of formula (1), such as2,5-bishydroxymethylfuran, as a curing accelerator. The methylol groupof the 2,5-bishydroxymethylfuran has high reactivity and, on contactwith a curing agent, such as phosphoric acid, undergoes condensationreaction with a methylol group, etc. of the binder to thereby acceleratethe curing reaction of the binder. Further, the methoxy group or ethoxygroup of 2,5-bismethoxymethylfuran or 2,5-bisethoxymethylfuran undergoeshydrolysis to a hydroxyl group on contact with a curing agent, such asphosphoric acid, and the thus formed hydroxyl group acts in the samemanner as described above to accelerate the curing reaction of thebinder.

Mold making by the use of the binder composition of the presentinvention achieves an increased curing rate of the binder to provide amold having an improved initial strength. Therefore, after filling apattern with a sand composition containing the binder composition, amold can be removed from the pattern in a shortened period of time. Thismeans a pattern for mold making can be used efficiently to obtainimproved productivity. Further, because the curing rate can beaccelerated by altering the composition of the binder compositionitself, there is no need to increase the amount of a curing agent or touse a large amount of a highly acidic curing agent. Therefore, moldingmaking can be carried on in a satisfactory working environment.

The curing agent composition for mold making of the present inventioncontains a sulfur-containing compound and a phosphorus-containingcompound at such a specific sulfur to phosphorus weight ratio that theweight ratio of the sulfur-containing compound, which serves to improvethe curing rate, can be controlled. When the binder composition of thepresent invention and the curing agent composition of the presentinvention are used in combination with a granular refractory material inmold making, a high curing rate of the binder can be assured even with areduced content of the sulfur-containing compound in the curing agentcomposition because the binder composition contains a curingaccelerator. With the sulfur-containing compound content being soreduced, generation of poisonous gas, such as sulfur dioxide, duringmold making is minimized to prevent deterioration of the workingenvironment. Compared with use of a phosphorus-containing compoundalone, the combined use of a phosphorus-containing compound and asulfur-containing compound results in reduction in the requisite amountof the phosphorus-containing compound. As a result, accumulation of alarge quantity of phosphorus in repeatedly reclaimed sand can be avoidedso that the reclaimed sand can be prevented from absorbing aconsiderable amount of moisture, which ultimately excludes thepossibility that the mold strength obtained from reclaimed sand may havereduced strength. Development of casting defects, such as pinholes,attributed to the presence of a large amount of accumulated phosphorusin the casting mold, can also be prevented.

While the invention has been described in detail and with reference tospecific examples thereof, it will be apparent to one skilled in the artthat various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A binder composition for mold making whichcomprises:(a) a binder comprising an acid-curable resin and (b) from 0.5to 63.0% by weight, based on the binder composition, of at least onecuring accelerator selected from compounds represented by formula (1):##STR5## wherein X₁, X₂ each independently represent a hydrogen atom, amethyl group or an ethyl group, and wherein said acid-curable resin isat least one compound selected from the group consisting of aphenol/aldehyde polycondensate, a urea/aldehyde polycondensate, and aco-condensate of said phenol/aldehyde and said urea/aldehydepolycondensates.
 2. The binder composition of claim 1, wherein saidcuring accelerator is present in an amount of from 1.8 to 50.0% byweight.
 3. The binder composition of claim 1, wherein said aldehyde isselected from the group consisting of formaldehyde, glyoxal andfurfural.
 4. The binder composition of claim 1, wherein said phenol isselected from the group consisting of phenol, resorcinol, bisphenol A,bisphenol F, a compound represented by formula (2): ##STR6## wherein R₁represents a hydrocarbon group having from 1 to 10 carbon atoms, andacompound represented by formula (3): ##STR7## wherein R₂ and R₃ eachindependently represent a hydrocarbon group having from 1 to 10 carbonatoms.
 5. The binder composition of claim 1, wherein said bindercomposition has a nitrogen content of from 0.1 to 6.0% by weight, basedon the weight of the binder composition.
 6. The binder composition ofclaim 1, wherein said acid-curable resin is a phenol/aldehydepolycondensate obtained by condensing an aldehyde with a phenolicmonomer in a proportion of from 2 to 40% by weight, based on thecombined weight of the aldehyde and phenolic monomer.
 7. The bindercomposition of claim 1, wherein said binder composition has a watercontent of from 0.5 to 30% by weight, based on the weight of the bindercomposition.
 8. The binder composition of claim 1, wherein said curingaccelerator is 2,5-bishydroxymethylfuran.
 9. A binder/curing agentcomposition for casting mold making which comprises:(i) a bindercomposition comprising:(a) a binder comprising an acid-curable resin,and (b) from 0.5 to 63.0% by weight, based on the total weight of binder(a) and curing accelerator (b), of at least one curing acceleratorselected from compounds represented by formula (1): ##STR8## wherein X₁,X₂ each independently represent a hydrogen atom, a methyl group or anethyl group; and (ii) a curing agent composition comprising aphosphorus-containing compound and a sulfur-containing compound at sucha weight ratio that a weight ratio of sulfur atoms to the total weightof phosphorus atoms and sulfur atoms is from 0.01 to 0.7, and whereinsaid acid-curable resin is at least one compound selected from the groupconsisting of a phenol/aldehyde polycondensate, a urea/aldehydepolycondensate, and a co-condensate of said phenol/aldehyde and saidurea/aldehyde polycondensates.
 10. The binder/curing agent compositionof claim 9, wherein said phosphorus-containing compound is at least onecompound selected from the group consisting of phosphoric acid,condensed phosphoric acid, a phosphoric ester, and a phosphate.
 11. Thebinder/curing agent composition of claim 9, wherein said weight ratio ofsulfur atoms to the total weight of phosphorus atoms and sulfur atoms isfrom 0.03 to 0.6.
 12. The binder/curing agent composition of claim 9,wherein said curing accelerator (b) is present in an amount of from 1.8to 50.0% by weight based on the total weight of binder (a) and curingaccelerator (b).
 13. The binder/curing agent composition of claim 9,wherein said aldehyde is selected from the group consisting offormaldehyde, glyoxal and furfural.
 14. The binder/curing agentcomposition of claim 9, wherein said phenol is selected from the groupconsisting of phenol, resorcinol, bisphenol A, bisphenol F, a compoundrepresented by formula (2): ##STR9## wherein R₁ represents a hydrocarbongroup having from 1 to 10 carbon atoms, anda compound represented byformula (3): ##STR10## wherein R₂ and R₃ each independently represent ahydrocarbon group having from 1 to 10 carbon atoms.
 15. Thebinder/curing agent composition of claim 9, wherein said binder/curingagent composition has a nitrogen content of from 0.1 to 6.0% by weightbased on the total weight of binder (a) and curing accelerator (b). 16.The binder/curing agent composition of claim 9, wherein saidacid-curable resin is a phenol/aldehyde polycondensate obtained bycondensing an aldehyde with a phenolic monomer in a proportion of from 2to 40% by weight, based on the combined weight of aldehyde and phenolicmonomer.
 17. The binder/curing agent composition of claim 13, whereinsaid binder/curing agent composition has a water content of from 0.5 to30% by weight, based on the total weight of binder (a) and curingaccelerator (b).
 18. The binder/curing agent of claim 9, wherein saidcuring accelerator is 2,5-bishydroxymethylfuran.
 19. A sand compositionfor mold making which comprises a granular refractory material, thebinder composition of claim 1 and a curing agent for curing the bindercomposition.
 20. The sand composition of claim 19, wherein said curingagent is a phosphorus-containing compound, a mixture of aphosphorus-containing compound and a sulfonic acid compound, a mixtureof a phosphorus-containing compound and sulfuric acid, or a mixture of aphosphorus-containing compound, a sulfonic acid compound, and sulfuricacid.
 21. The sand composition of claim 19, wherein said curing agent isselected from the group consisting of phosphoric acid, condensedphosphoric acid, a phosphoric ester, and a phosphate.
 22. A sandcomposition for mold making which comprises a granular refractorymaterial and the binder/curing agent composition of claim
 9. 23. Aprocess for making a mold which comprises:charging a pattern with thesand composition of claim 19; and allowing the binder contained in thesand composition to cure.
 24. A process for making a mold whichcomprises:charging a pattern with the sand composition of claim 22; andallowing the binder contained in the sand composition to cure.